1. Field of the Invention
The present invention relates to a fine scanning mechanism for an atomic force microscope (to be abbreviated to "AFM" hereinafter). More particularly, the present invention relates to a fine scanning mechanism which uses a cylindrical piezoelectric element which can be displaced three-dimensionally (XYZ) and a bimorph piezoelectric element which can be displaced one-dimensionally (Z).
2. Description of the related Art
It is preferable that a fine scanning mechanism for an AFM comprises a cylindrical piezoelectric element which can be easily manufactured because its shape is simple, which reveals improved rigidity and which can be threedimensionally displaced. As an alternative to this, it is suitable to employ a bimorph piezoelectric element because it is able to produce a large displacement with a low voltage and it can be one-dimensionally displaced.
Hitherto, as the fine scanning mechanism which employs the cylindrical piezoelectric element which can be threedimensionally displaced or the bimorph piezoelectric element which can be one-dimensionally displaced, the following structures have been available:
(1) A structure for an AFM which employs a cylindrical piezoelectric element for three-dimensionally displacing a sample and which has been disclosed in 0.Marti, B.Drake and P.K.Hansma; Appl. Phys. Lett., Vol. 51, No. 7, pp. 484-486 (1987) and O.Marti, B.Drake, S.Gould and P.K.Hansma; J. Vac. Sci. Technol. A, Vol. 6, No. 2, pp. 287-290 (1988);
(2) A structure for an AFM which employs a cylindrical piezoelectric element for three-dimensionally displacing a probe and which has been disclosed in P.J.Bryant, R.G.Miller and R.Yang; Appl. Phys. Lett., Vol.52, No.26, pp.2233-2235 (1988) and P.J.Bryant, R.G.Miller, R.Deeken, R.Yang and Y.C.Zheng; Journal of Microscopy, Vol. 152, Pt 3, pp.871-875 (1988);
(3) A fine scanning mechanism which employs a bimorph piezoelectric element which can also be used in a fine scanning mechanism for the AFM, which is used in, for example, a near-field optical-scanning microscope (NFOM) and which has been disclosed in U.Durig, D.W.Pohl and F.Rohner; J. Appl. Phys., Vol.59, No.10, pp.3318-3327 (1986); and
(4) A fine scanning mechanism for an AFM for observing the discharge distribution image by applying microvibrations to the probe by using a bimorph piezoelectric element and which has been disclosed in J.E.Stern, B.D.Terris, H.J.Mamin and D.Rugar; Appl. Phys. Lett., Vol.53, No.26, pp.2717-2719 (1988) and B.D.Terris, J.E.Stern, D.Rugar and H.J.Mamin; Phys. Rev. Lett. Vol.63, No.24, pp. 2669-2672 (1989). The above-described fine scanning mechanisms are shown in FIGS. 9A.to 9E.
The fine scanning mechanism shown in FIG. 9A comprises: a cylindrical piezoelectric element 100 to which a sample tray 500, on which a sample 510 is placed, is secured; a cantilever 300 having a second probe 410 composed of, for example, a diamond stylus; and a first probe 110 made of, for example, metal and acting to detect the deflection of the cantilever 300. The distance between the first probe 110 and the cantilever 300 can be adjusted by a fine adjustment screw 311. The first probe 110, the cantilever 300 and the fine adjustment screw 311 are provided for a lever holder 312. The cylindrical piezoelectric element 100 is composed of a cylindrical piezoelectric material 101 and an electrode 102. The electrode 102 is composed of four sections of electrodes 1021, 1022, 1023 and 1024 formed on the outer surface of the cylindrical piezoelectric material 101 parallel to the axis of cylinder and another electrode 1025 formed on the entire inner surface of the cylindrical piezoelectric material 101. When triangular voltages Vx+, Vx-, Vy+ and Vy- are applied to the electrodes 1021, 1022, 1023 and 1024 and as well as voltage Vz for Z-directional scanning is applied to the electrode 1025, the second probe 410 three-dimensionally scans the surface of the sample 510 attached to the sample tray 500. The deflection of the cantilever 300 that takes place due to atomic force acting between the second probe 410 and the surface of the sample 510 when the above-described three-dimensionally scanning is performed is detected by the first probe 110.
The fine scanning mechanism shown in FIG. 9B comprises: a cylindrical piezoelectric element 100 to which a first probe 110 made of, for example, metal, a cantilever 300 and a second probe 410 made of, for example, metal are attached; and the sample tray 500. When the cylindrical piezoelectric element 100 threedimensionally scans the sample similarly to the fine scanning mechanism shown in FIG. 9A, the first probe 110, the cantilever 300 and the second probe 410 act in a synchronized manner so that the second probe 410 three-dimensionally scans the surface of the sample 510 attached to the sample tray 500. Thus, the three-dimensionally scanning fine scanning mechanism for an AFM is realized.
The fine scanning mechanism shown in FIGS. 9C and 9D comprises a bimorph piezoelectric element 200; a sample tray 500 attached to the bimorph piezoelectric element 200; and a second probe 410 manufactured by applying aluminum to, for example, a diamond or crystal chip the front portion of which is sharpened. The bimorph piezoelectric element 200 is composed of bimorph piezoelectric elements 2001, 2002, 2003, 2004 and 2005. The defection the piezoelectric elements 2001 and 2002 creates an X-directional displacement, while the deflection of the piezoelectric elements 2003 and 2004 creates a Y-directional displacement. As a result, the sample 510 attached to the sample tray 500 is two-dimensionally scanned. Furthermore, a Z-directional displacement is given to the second probe 410 by the deflection of the piezoelectric element 2005 so that the surface of the sample 510 is three-dimensionally scanned. Thus, a fine scanning mechanism for a NFOM is constituted. Since the above-described fine scanning mechanism is able to perform the three-dimensional scanning operation, it can be applied as the fine scanning mechanism for the AFM.
The fine scanning mechanism shown in FIG. 9E comprises the sample tray 500 which can be three-dimensionally scanned; and the bimorph piezoelectric element 200 for vibrating the second probe 410 made of metal with respect to the position of the sample 510 attached to the sample tray 500. Thus, a fine scanning mechanism for an AFM is constituted which is capable of observing a charge distribution image in such a manner that an optical beam reflected from the second probe 410 is received by a sensor 20 via an optical fiber 10.
However, the above-described conventional fine scanning mechanisms encounter the following problems:
The fine scanning mechanism 1000 shown in FIG. 9A encounters a problem in that the size of the sample tray 500 attached to the cylindrical piezoelectric element 100 is limited by the diameter of the cylindrical piezoelectric element 100. Therefore, if the sample 510 has a large size, it cannot be observed by the AFM. What is worse, since the piezoelectric material 101 forming the cylindrical piezoelectric element 100 suffers from poor mechanical rigidity, there arises a risk that the cylindrical piezoelectric element 100 can be damaged when the sample 510 is attached to the sample tray 500. Therefore, the sample 510 cannot easily be attached/detached from the sample tray 500.
The fine scanning mechanism shown in FIG. 9B causes difficulty in presetting, adjustment and setting operations so as to make the distance between the first probe 110 and the cantilever 300 fall within the tunnel region. The distance between the first probe 110 and the cantilever 300 in the tunnel region is an extremely short distance, on the order of 10 angstrom. In consequence, the initial adjustment work cannot easily be completed. Furthermore, it is very difficult to perform re-adjustment operation if the distance has been changed in accordance with a lapse of time or after the first probe 110 has been changed because the first probe 110 had made contact with the cantilever 300.
The fine scanning mechanism shown in FIGS. 9C and 9D have a problem in that the structure is too complicated and it cannot easily be manufactured. What is even worse, the obtainable reproducibility as a fine scanning mechanism is unsatisfactory. Since the sample tray 500 is secured to the displaceable portion of the bimorph piezoelectric element 200, it is difficult to attach the sample 510, and the bimorph piezoelectric element 200 will be deformed or broken when the sample 510 is attached.
The fine scanning mechanism shown in FIG. 9E has a problem similarly to that shown in FIG. 9A since the sample tray 500 must be moved.
That is, the conventional fine scanning mechanisms for an AFM have the following problems: the cylindrical piezoelectric element 100 or the bimorph piezoelectric element 200 will be deformed or broken when the sample 510 is attached; the sample 510 cannot easily be attached or detached from the sample tray 500; it is difficult to set the distance from the first probe I10 to the cantilever 300; and a fine scanning mechanism revealing excellent reproducibility cannot be manufactured.